SmartTable Custom Action Problem for displaying Icons

### Issue type

**I'm submitting a ...** (check one with "x")

* [X] bug report
* [ ] feature request
* [ ] question about the decisions made in the repository

### Issue description

**Current behavior:**

If you create custom action other than edit,remove,add. And if you add an icon, you will see that there is a problem of display. The icon is not in a row, but between rows.

**Expected behavior:**
The icon has to be in a row

**Steps to reproduce:**
Use smarttable, create custom action, add an icon to this action. Look the icon


```
actions: {
add: false,
edit: false,
delete: false,
columnTitle: "Actions",
custom: [{ name: 'ourCustomAction', title: '' }],
position: 'right',
},
columns: {
id: {
title: 'ID',
type: 'number',
width: '7%'
},
....
...
```

### Other information:
Version : 2 Nov 2020